In an anthropological forum, there was once a view that because Latin, Greek, Sanskrit (also Celtic IIRC) are Mora-timed, they are divided into one subgroup. However, "syllable-timed" Iranian and "stress-timed" Balto-Slavo-Germanic are classified into another subgroup. That view also argues that languages may develop in the direction of Mora-Timed>Syllable-Timed>Stress-Timed, and Mora-Timed is closely related to long vowels.
However, we know that in the phylogenetic tree model, this is unlikely. First of all, Iranian languages (at least well-attested languages like Avestan, Persian, Pashto etc.) and Sanskrit must consist one certain subgroup. Secondly, the model that classifies Latin, Greek and Sanskrit into one subgroup, but Balto-Slavo-Germanic into another, except for one Schleicher's tree, most other trees are not like this. For example, in Thomas Olander's tree model, Italo-Celtic is the third to split after Anatolian and Tocharian, predating Germanic and Balto-Slavic.
Therefore, I have some doubts about the relationship between mora-timed languages, quantitative metre and long vowels.
First of all, are mora-timed and long vowels directly related? Many modern Romance languages have lost the opposition of long and short vowels in Latin and PIE, so they have become syllable-timed. But Proto-Iranian, Proto-Balto-Slavic, and Proto-Germanic all retain the opposition of long and short vowels. The following linguistic forum also recognizes that Lithuanian is a Mora-timed language, just like classical Latin, Greek, Sanskrit and Japanese. Therefore, in Balto-Slavo-Germanic, are there more Mora-timed languages (whether historical or modern)?
My second doubt is the relationship between Mora-timed and quantitative verse. According to Wikipedia, in addition to classical Latin, Greek, and Sanskrit, classical Persian, classical Arabic and Old Church Slavonic also use quantitative metre. However, Persian is a stress-timed language. On the contrary, although Japanese is a Mora-timed language, according to Britannica, Japanese often uses syllabic verse.